EEG power spectrum typical of vascular dementia in a subgroup of Alzheimer patients.

A statistical comparative study was carried out between two subgroups of patients with dementia, i.e. 22 with Alzheimer's dementia (AD, 44% of the entire Alzheimer group examined) and 36 with vascular dementia (VaD, 97% of the entire vascular group). The selection of the two subgroups was based on a similar EEG spectral profile in the rest eyes closed condition: a great increase in low frequency powers and a dominant activity in the 6.5-12 Hz band. The aim was to identify any possible difference between the two groups analysing the spectral descriptors, of the two conditions eyes closed and open, the demographic figures and the mental deterioration scores. The results are as follows: (i) the spectral profiles and their numerical descriptors of the AD subgroup patients are not distinguishable from the same parametric figures of the VaD patients; (ii) the spectral analysis becomes useful in differentiating the two types of dementia when a dynamic EEG is processed, i.e. the power ratio of recordings during eyes closed and open; (iii) a more severe mental deterioration, especially in attention and spatial and temporal orientation was found in the AD group as compared to the VaD. The findings are explained in the light of the changes in neural mechanisms which underlie both the alpha and slow rhythms.